1. Field of the Invention
The present invention generally relates to circuit device packages. More particularly, this invention relates to circuit modules that require circuitry during development of the module that is later unneeded in production units of the module, wherein the circuitry is mounted on a flexible circuit that permits removal of the circuitry from the module without otherwise requiring modifications to the module.
2. Description of the Related Art
The continuous effort to reduce the size of circuit board assemblies has promoted the use of advanced packaging technologies such as multichip modules (MCM), including ball grid arrays (BGA). Circuit devices, typically surface-mount technology (SMT) components, are attached with solder to a chip carrier, often a laminate substrate such as a high-density printed circuit board (PCB). The solder may be initially present in the form of solder bumps that are formed on the devices and then reflowed to form solder joint connections that attach the devices to the chip carrier. In the case where the chip carrier is a PCB, it is usually desirable to underfill any flip chips on the chip carrier with a filled epoxy to ensure the reliability of the solder joint connections. The resulting MCM may be overmolded before being mounted to a motherboard, such as by reflowing solder bumps formed on the lower surface of the chip carrier. Finally, the motherboard assembly may be overmolded to protectively encase the MCM as well as any other MCM's or other circuit components mounted to the motherboard.
An example of an application for MCM's as described above is powertrain control modules (PCM's) for automotive applications. Instrumentation circuitry is often included in PCM's for emulation carried out during development and qualification of the PCM to assess the performance of an MCM mounted thereto. Current instrumentation techniques may require a calibration random access memory integrated circuit (RAM IC), a controller area network (CAN) IC, a connector with multiple signal lines, and supporting circuitry, all of which must be accommodated on the motherboard. Where practice prohibits altering a PCM design or its motherboard layout after qualification, the area on a PCM motherboard for the instrumentation circuitry must be carried on production PCM units long after there is any need for the instrumentation circuitry. The result is wasted motherboard real estate, increased cost, and the potential for noise generated because of the open signal lines of the instrumentation circuitry connector.
In view of the above, it can be appreciated that it would be desirable to eliminate the need to accommodate instrumentation circuitry on production units of a PCM motherboard and other motherboards on which MCM's are mounted.